The second (and more recently explored) mechanism that can give rise to social preferences is population structure.
When players with similar preferences are more likely to interact with each other, evolution may give rise to behavior consistent with Homo moralis [1]}. For pairwise interactions, this type of player maximizes a linear combination of the material payoff and the payoff the player would obtain if the co-player adopted the same strategy. While we focus on well-mixed populations throughout most of the main text, we describe in the Methods section that population structure can also have a positive effect within our learning framework.
